Driven by the rapidly-growing field of hybrid and electric vehicles, there is an increasing demand for lithium-ion batteries (LIBs) characterized by high energy density, long cycle life, and low manufacturing cost. One of the most widely used anode materials in LIBs, graphite, possesses a theoretical specific capacity of only about 370 mAh/g, limiting the specific energy of LIBs. Recently, silicon (Si) has been regarded as one of the most promising anode materials for high-performance LIBs, due to its exceptionally high specific capacity (>4200 mAh/g). However, as an electrode material choice, SI suffers from several drawbacks, including a relatively low electrical conductivity, a volume change exceeding 300% upon lithium-ion insertion and/or deinsertion, and a rapid capacity fade. Perhaps chief among these issues, the dramatic volume change can result in the pulverization of the Si substrate, resulting in a loss of the electrical contact therewith and an unstable solid electrolyte interphase (SEI) layer. To overcome these disadvantages, various nanostructured Si materials have been developed, including Si nanoparticles, nanoporous Si, nanowires, core-shell structures, nanotubes, Si/carbon nanocomposites, and Si conformed in a conducting hydrogel. However, these materials still have some drawbacks, such as unsatisfactory cycling life, low capacity, low Coulombic efficiency, and complicated, expensive synthesis.
Recently, graphene/Si composite materials have been extensively studied by encapsulating Si nanoparticles within graphene nanosheets to create empty space to accommodate the volume change, buffer the mechanical stress, and improve the electrical conductivity. Graphene/Si composites may be prepared by drying an aqueous suspension of Si nanoparticles and graphene oxide (GO) and then thermally reducing the GO. The challenge of developing a uniform graphene/Si composite lies in the Si nanoparticles tending to aggregate in the aqueous solution, resulting in the inhomogeneous mixing of GO and Si. Creating an oxide layer on the Si nanoparticles and further functionalizing the Si nanoparticles to enhance their dispersion and the interaction between GO and Si can result in more uniform graphene/Si composites. Graphene/Si composites prepared using aminopropyltriethoxysilane-functionalized Si nanoparticles instead of conventional Si nanoparticles showed good performance as anodes in LIBs. However, the SiO2 layer of a Si nanoparticle, acting as both an electrical insulator and a Li+ diffusion barrier, has a negative impact on the electrochemical performance of Si-based electrodes yielding lower reversible capacity and decreased Coulombic efficiency. Thus, the use of a SiO2 layer solves the dispersion problem but at a cost of performance and a hindrance to the preparation of uniform graphene-encapsulated Si composites without a SiO2 passivation layer.
Thus, there remains a need for an improved graphene based silicon-containing electrolytic material. The present novel technology addresses this need.